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What is the Difference between Hot Runner and Cold Runner Injection Molding?

Home » FAQ » What is the Difference between Hot Runner and Cold Runner Injection Molding?

Hot Runner Molds

Two plates make up a hot runner mold. These plates are heated through the use of a manifold system. Both externally and internally heated hot runners are available for use. For materials that are particularly sensitive to heat, externally heated molds are preferred. When enhanced flow control is desired, internally heated molds are the better option. The methods available to heat runners include heating rods, coils, and heating pipes. A hot runner system keeps material in a molten state during the duration of the runner process until it flows into the mold cavity.

Cold Runner Molds

In a cold runner system, the runners and the molds are maintained at the same temperature. Within this system, two or three plates are contained within the mold. The two plate system is easier to use, but requires an injection system to remove the part from the mold. Within a three-plate system, the runner functions on a separate plate. Therefore, it can be ejected separately from the runner. A three-plate cold runner mold allows for flexibility in design. To ensure the mold is not under filled in that the material fills the part properly, the runner dimension must be larger than the part within this system.

How does a hot runner system work?

A hot runner mold consists of two plates that are heated by means of a manifold system. Both internally heated and externally heated hot runners are available. When more flow control is required, internally heated molds are the ideal choice. When materials are extra sensitive to heat, the preferred option is to use externally heated molds. There are various methods available for heat runners, including heating pipes, coils, and heating rods. Materials are kept in a molten condition during the runner process by means of a hot runner system until the material flows into the mold cavity.

How does a cold runner system work?

Cold runners consist of an unheated channel that is used to convey molten plastic into a mold cavity after it is dispensed from the nozzle. As a result, the channel of cold runners must be larger, necessitating a greater flow of plastic through each cycle. As a result, you could run up the cost higher than a hot runner assembly process if you need to shoot a large number of parts while running through several iterations to arrive at the correct design.

If the cold runners are not recycled, they can create waste. However, this system is easier and less expensive to maintain than a hot runner system. Another advantage of the cold runner systems is the ability to handle a wide-array of polymers, particularly specialty polymers. This system can also accommodate quick color changes.